I would recommend root tabs.I use them in only lowlight,plain gravel,or sand tanks.I just recently started using them with the occasional dose of excel and have noticed a lot more growth in the plants.Just my experience.
I experienced the opposite when my tank was low light...unless you really have a plant that takes in a lot of nutrients from it's roots (i.e. swords) I don't think it makes a huge difference. JME though...